This invention is directed to a method for the manufacture of thermoformed articles comprising a form-retaining thermoformable substrate and a flexible web coverstock. More specifically, the invention is directed to a process and apparatus in which multiple steps are performed in a single, integrated process.
It has long been known to manufacture form-retaining parts from sheets of thermoformable material. Exemplary of such technology is that disclosed in U.S. Pat. No. 4,243,456 to Cesano. Therein is taught the use of, for example, thermoformable sheets comprising polyolefin and woodflour. Such sheets can be produced by the extrusion method disclosed in U.S. Pat. No. 4,228,116 to Columbo et al. Numerous additional thermoformable sheetstocks comprising thermoplastic materials are well known to the skilled of the art and are commercially available. Amongst the many thermosettable sheetstock materials are fiber reinforced sheet molding compound (SMC) and the like.
Various different thermoforming processes are known to the skilled of the art and include, for example, compression molding and the like. A choice of appropriate thermoforming processes will depend, in part, on the nature of the thermoformable sheetstock employed and on the configuration and desired properties of the finished product.
Frequently it is desirable to provide the thermoformed product with a coverstock material. The coverstock material may be, for example, a woven or non-woven fibrous material laminated to a surface of the thermoformed product for decorative and/or functional purposes. Other coverstock materials include, for example, a plastic sheet laminated to a surface of the thermoformed product, again for decorative purposes and/or for functional purposes, such as moisture or abrasion protection. Such coverstock materials can be laminated to the theroformable substrate sheetstock either prior to the thermoforming step or, more typically, during the thermoforming step. Thus, for example, in a typical thermoforming process a sheet of thermoformable material is positioned in a molding tool, such as by laying it over the lower member of a pair of matched forming dies, and subsequently a sheet of the coverstock material is positioned on top of the thermoformable sheetstock. In this way the sheetstock is thermoformed into the desired product configuration and the coverstock is laminated thereto in a single step. Alternatively, the coverstock can be laminated to the sheetstock prior to the thermoforming step. While this simplifies and reduces the labor of the thermoforming step, there may be an even greater, offsetting increase in the labor associated with the separate lamination step if that involves loading and positioning the substrate sheetstock and coverstock together in a laminating device. In some instances, however, it is possible to laminate the coverstock to the substrate sheetstock during manufacture of the substrate sheetstock with considerable efficiencies in time and labor. Even in this case though, there remains the labor and time requirements associated with the thermoforming step, plus that associated with removing the thermoformed product from the thermoforming mold and transporting it to any one or more subsequent stations, such as trimming stations at which excess material is trimmed away, parting lines and apertures are cut into the part, etc.
It is an object of the present invention to provide a process and apparatus which enable an improvement in the labor and cost efficiencies associated with thermoforming form-retaining products comprising a thermoformable substrate and a flexible web coverstock laminated thereto. These and other advantages and features of the invention will be better understood from the following disclosure.